Studies of aerobic energy metabolism were continued to elucidate mechanisms of electron transfer in the respiratory chains of Entamoeba histolytica and Giardia lamblia. Purification and preliminary characterization of the oxidoreductases in these parasites was done by affinity chromatography and gel electrophoresis. Specific activity of the NAD(P)H oxidoreductases of G. lamblia was increased 50-fold, and separation of the enzymatically active proteins by gel electrophoresis yielded 6 bands. Flavin was present in a 1:1 molar ratio to protein. These enzymes provide a mechanism for oxidation of NADH generated during glycolysis since both mitochondria and lactate dehydrogenase are absent in these eukaryatic protozoans. Studies were continued on the effect of heme depletion of the respiration of cultured murine erythroleukemia cells and isolated rat hepatocytes. Mammalian studies were initiated on the effect of psychoactive drugs on oxidative phosphorylation in mitochondria isolated from rat brain and liver. Reserpine acts as a classical uncoupling agent only when dissolved in organic solvents to facilitate penetration through the mitochondrial membranes. Pargyline and the biogenic amines do not affect the four states of mitochondrial respiration.